A shoe or boot with wheels attached at the bottom, used for skating on dry land instead of ice. The term is generally applied to skates with two pairs of wheels arranged under the ball and heel respectively.
The original prototypes of the 1800s were in-line designs like today's modern inline skates. Due to the design of the boot and wheels, however, it was difficult or impossible to turn on the skates without stopping. Skating enjoyed its first commercial success in a German beer hall near Berlin, where they enabled the waitresses to quickly serve patrons in the huge tavern.
An advance came in 1863 when James Plimpton added springs to a design with two sets of wheels attached at the bottom, like the chassis of a car. This design allowed the wearer to turn in a smooth curve. Several waves of popularity followed in the United States and Europe, losing steam with the onset of the two World Wars, but reviving afterward. Roller rinks were set up to allow fans to roller-skate together, similar to ice skating at ice rinks.
Roller skates have several key niches in Americana. The roller-skating wait staff of 1950s drive-in hamburger joints are a visual shorthand for the time, and are often a feature of movies about the period. The "sports entertainment" spectacle of Roller Derby was popular through the 1950s and 1960s. The roller rink enjoyed a revival in the 1970s in Frankenstein combination with the discotheque, the time or roller-discos. And, who could forget the classic novelty tune "You can't roller skate in a buffalo herd by Roger Miller?
The classic roller skate was likely supplanted for good in 1983 when Rollerblade, Inc. introduced an innovative new in-line skate design, returning roller skates to the form of their 1800s origins. (As the long-time dominant brand, "Rollerblade" is often used as a generic term for inline skates, much as brand names "Aspirin" or "Styrofoam" are used as generics.) The classic two-pair roller-skate wheel design is now called a "quad skate" to distinguish it from in-line skates.
Roller skate was also a Citizens Band radio reference to a compact or sub-compact car, alluding to their small size and often cheap construction. A "pregnant roller skate" referred to a Volkswagen Beetle.
Roller skate may be used as a verb: to locomote while wearing a pair of roller skates, with at lest a modicum of skill.
Sources included http://inventors.about.com/library/weekly/aa050997.htm.